In this post we will configure Site-to-Site IPSEC VPN between a Cisco IOS Router and ASA Firewall. ASA configuration is not much different from Cisco IOS with regards to IPSEC VPN since the fundamental concepts are the same. Let’s start our LAB example and we’ll see how it’s done.

Consider the following diagram. The first site (Remote1) is equipped with a Cisco ASA firewall (any model) and the second site (Remote2) is equipped with a Cisco Router. Remember that a Cisco ASA firewall is by default capable to support IPSEC VPN but a Cisco Router must have the proper IOS software type in order to support encrypted VPN tunnels.

Equipment Used in this LAB:

• ASA 5510 – Cisco Adaptive Security Appliance Software Version 8.0(3)

• Cisco Router 2801 – C2801-ADVIPSERVICESK9-M Version 12.4(9)T4

Scenario:

LAN of Remote1 must be connected to LAN of Remote2 via VPN Tunnel. The most usual scenario is that the WAN cloud is the Internet, so secure connectivity shall be provided between the two LAN networks over the Internet.

First of all we shall make sure that the outside interfaces of ASA and router must be reachable over the WAN. Now let’s start IPSEC VPN configuration.

Cisco ASA Configuration

First I started ASA configuration.

I’ve created an Access list, which will match the interesting traffic which is the traffic to be encrypted. If source is 192.168.3.0/24 and destination is 192.168.4.0/24, then traffic will be matched by the access list as “interesting traffic” and will be encrypted and pass through the tunnel.

ASA(config)# access-list vpn extended permit ip 192.168.3.0 255.255.255.0 192.168.4.0 255.255.255.0

!IKE PHASE #1
! I’ve created a phase1 policy. This policy provides secured process of exchanging Keys.
ASA(config)# crypto isakmp policy 1

! For authentication I used Pre-shared. This method is most frequently used today.
ASA(config)# authentication pre-share

!For encryption I used 3des.
ASA(config)# encryption 3des

! Hashing md5.
ASA(config)# hash md5

! I used second group of diffie-hellman. Group1 is used by default. The most secured is Group5.
ASA(config)# group 2

! configure crypto key. The keys must match to each other between peers. Otherwise Phase1 will not be completed.
ASA(config)# crypto isakmp secretsharedkey address 192.168.2.2

NOTE: Crypto key is hidden in ASA configuration. If we look at configuration, it will be shown in following way.
tunnel-group 192.168.2.2 ipsec-attributes
pre-shared-key *

! Activate policy on Outside interface.
ASA(config)# crypto isakmp enable outside

! IKE PHASE #2- VPN Tunnel is established during this phase and the traffic between VPN Peers is encrypted according to the security parameters of this phase.

! I created Transform-set, by which the traffic will be encrypted and hashed between VPN peers.
ASA(config)# crypto ipsec transform-set ts esp-3des esp-md5-hmac

! Apply the access list created earlier for matching the interesting traffic.
ASA(config)# crypto map vpn 10 match address vpn

! I indicated address of Remote2 peer public outside interface.
ASA(config)# crypto map vpn 10 set peer 192.168.2.2

! Apply also the transform-set.
ASA(config)# crypto map vpn 10 set transform-set ts

! Attach the already created Crypto-map and VPN to outside interface.
ASA(config)# crypto map vpn interface outside

ASA configuration is completed here (regarding the VPN config of course). Now let’s start Router Configuration below.

Cisco Router Configuration

ISAKMP Phase 1

! Enter crypto-isakmp policy configuration mode for configuring crypto isakmp policy.
Router(config)# crypto isakmp policy 10

! Turn on 3des as an encryption type.
Router(config)# encr 3des

! I indicated MD5 as a hashing type.
Router(config)# hash md5

! I indicated pre-share authentication.
Router(config)# authentication pre-share

! I used second group of diffie-hellman. group1 is used by default.
Router(config)# group 2

! I defined peer key same as ASA site.
Router(config)# crypto isakmp secretsharedkey address 192.168.1.2

It’s not necessary to match policy numbers. The most important is to match corresponding parameters of policy. Otherwise negotiation of Phase1 will not be successful.

! Access list for matching interesting traffic.
Router(config)# ip access-list extended vpn
Router(config)# permit ip 192.168.4.0 0.0.0.255 192.168.3.0 0.0.0.255

ISAKMP PHASE 2
!
! Create IPSEC transform-set, by which the mechanism of hashing and encryption is determined, by which the traffic will be hashed/encrypted in VPN tunnel later.
Router(config)# crypto ipsec transform-set ts esp-3des esp-md5-hmac

! Enter into crypto-map configuration mode.
Router(config)# crypto map vpn 10 ipsec-isakmp

! Indicate IP address of peer.
Router(config)# set peer 192.168.1.2

! Indicate IPsec transform-set created above.
Router(config)# set transform-set ts

! Apply access list created above.
Router(config)# match address vpn

! Apply crypto-map to interface.
Router(config)# interface FastEthernet0/0
Router(config)# crypto map vpn

With this, VPN configuration is completed so let’s start verification.

! In the output below it is shown that ISAKMP PHASE1 is active, which means that negotiation of PHASE1 is completed successfully.

ASA# show crypto isakmp sa

Active SA: 1
Rekey SA: 0 (A tunnel will report 1 Active and 1 Rekey SA during rekey)
Total IKE SA: 1

1 IKE Peer: 192.168.2.2
Type : L2L Role : initiator
Rekey : no State : MM_ACTIVE

Router# show crypto isakmp sa
dst src state conn-id slot
192.168.1.2 192.168.2.2 MM_ACTIVE 1 0

! Checking ISAKMP PHASE2. Here we see that IPSec is working and the interesting traffic flows in VPN Tunnel.

ASA# show crypto ipsec sa
interface: outside
Crypto map tag: vpn, seq num: 10, local addr: 192.168.1.2

access-list vpn permit ip 192.168.3.0 255.255.255.0 192.168.4.0 255.255.255.0
local ident (addr/mask/prot/port): (192.168.3.0/255.255.255.0/0/0)
remote ident (addr/mask/prot/port): (192.168.4.0/255.255.255.0/0/0)
current_peer: 192.168.2.2

#pkts encaps: 344, #pkts encrypt: 344, #pkts digest: 344
#pkts decaps: 344, #pkts decrypt: 344, #pkts verify: 344
#pkts compressed: 0, #pkts decompressed: 0
#pkts not compressed: 344, #pkts comp failed: 0, #pkts decomp failed: 0
#pre-frag successes: 0, #pre-frag failures: 0, #framents created: 0
#PMTUs sent: 0, #PMTUs rcvd: 0, #decapsulated frgs needing reassembly: 0
#send errors: 0, #recv errors: 0

Router# show crypto ipsec sa

interface: FastEthernet0/0
Crypto map tag: vpn, local addr 192.168.2.2

protected vrf: (none)
local ident (addr/mask/prot/port): (192.168.4.0/255.255.255.0/0/0)
remote ident (addr/mask/prot/port): (192.168.3.0/255.255.255.0/0/0)
current_peer 192.168.1.2 port 500
PERMIT, flags={origin_is_acl,}
#pkts encaps: 344, #pkts encrypt: 344, #pkts digest: 344
#pkts decaps: 344, #pkts decrypt: 344, #pkts verify: 344
#pkts compressed: 0, #pkts decompressed: 0
#pkts not compressed: 0, #pkts compr. failed: 0
#pkts not decompressed: 0, #pkts decompress failed: 0
#send errors 0, #recv errors 0

VPN Tunnel is established and works.

Today I have stumbled upon an interesting technique from the Cisco Blog and Cisco Support Forum which is about defending an SQL injection using IPS, ASA or IOS firewall. I will concentrate on the ASA here to show you what you can do with this great device. Ofcourse what I will show works only for specific SQL attacks and is not an “ALL IN ONE” mechanism for preventing all SQL attacks. You should have a web application firewall in addition to ASA in my opinion if you want to have a full blown SQL and Web Application protection.

So basically the ASA uses regular expressions (regex) together with Modular Policy Framework to inspect specific HTTP data patterns in order to detect the SQL injection attack. It will basically check for the SQL command “UNION ALL SELECT”.

Below is the configuration as described on the Cisco support forum:

regex SQL_regex_1 “[uU][nN][iI][oO][nN]([%]2[0bB]|[+])([aA][lL][lL]([%]2[0bB]|[+]))?[sS][eE][lL][eE][cC][tT]“
regex SQL_regex_2 “[Ss][Ee][Ll][Ee][Cc][Tt](%2[0bB]|+)[^\r\x00-\x19\x7f-\xff]+(%2[0bB]|+)[Ff][Rr][Oo][Mm](%2[0bB]|+)”
!
class-map WebServers
match port tcp eq www
class-map type inspect http match-any SQL-map
match request body regex SQL_regex_1
match request body regex SQL_regex_2
!
policy-map type inspect http drop-SQL
parameters
body-match-maximum 3000
class SQL-map
drop-connection log
policy-map SQL-traffic
class WebServers
inspect http drop-SQL
!
service-policy SQL-traffic interface outside

We assume that our webserver is protected on a DMZ zone on the ASA. Traffic is coming from the outside so the service policy (SQL-traffic) is applied on the outside. Upon a regular expression match, the ASA will drop the HTTP connection and generate a log. The above is a just a starting point for SQL attack protection and can not defend against all attacks. For example if the SQL statement is Hex encoded or url encoded by the attacker, the regex will not detect it. Here is the link from Cisco forum for more information:

https://supportforums.cisco.com/docs/DOC-14890

After the introduction of Cisco ASA software version 8.3 last year, the device’s memory requirements for low-end models have been doubled. Many firewall administrators have been discouraged from this move from Cisco because they had to upgrade their firewalls RAM memory in order to upgrade to the newest versions. Upgrading the memory not only costs money but it imposes an operational hassle as well (network downtime, need to open-up the chassis etc). I get many questions from my readers about memory upgrade guides, so the links below might be helpful for some of you.

The following table shows the new memory requirements for all Cisco ASA 5500 models for software version 8.3 and later:

Cisco ASA Memory Requirements

The following video from Cisco shows you how to upgrade the memory chip on a Cisco ASA 5510 Firewall.

Upgrade Memory on Cisco ASA 5510 – Video

The following post from ccsplab shows some information for upgrading both the RAM and Flash memory on a Cisco ASA 5505 model.

Upgrade RAM and Flash on Cisco ASA 5505

The ASA 5500 series firewall can work as DHCP relay agent which means that it receives DHCP requests from clients on one interface and forwards the requests to a DHCP server on another interface. Usually the DHCP server is located in the same layer 3 subnet with its clients. There are situations however where we have only one DHCP server but several layer 3 networks exist (on different security zones on a Cisco ASA) and dynamic IP allocation is required for those networks as well. With the DHCP relay feature, we can connect the DHCP server on one network zone and have the firewall forward all DHCP requests from the other network zones to the DHCP server.

Configuration

!First identify the DHCP server and the interface it Is connected to
ciscoasa# conf t
ciscoasa(config)# dhcprelay server 10.1.1.100 DMZ
ciscoasa(config)# dhcprelay timeout 90

!Now enable the DHCP relay on the inside interface
ciscoasa(config)# dhcprelay enable inside

!Assign the ASA inside interface IP as default gateway for the clients
ciscoasa(config)# dhcprelay setroute inside

Usage Guidelines

You can add up to four DHCP relay servers per interface. You must add at least one dhcprelay server command to the ASA Firewall configuration before you can enter the dhcprelay enable command. You cannot configure a DHCP client on an interface that has a DHCP relay server configured.

You cannot enable DHCP relay under the following conditions:
• You cannot enable DHCP relay and the DHCP relay server on the same interface.
• You cannot enable DCHP relay and a DHCP server (dhcpd enable) on the same interface.

This article describes the user interface and access modes and commands associated with the operation of Cisco ASA 5500 firewall appliances. We assume that you know how to connect to the appliance using a console cable (the blue flat cable with RJ-45 on one end, and DB-9 Serial on the other end) and a Terminal Emulation software (e.g HyperTerminal), and how to use basic Command Line Interface.

SECURITY APPLIANCE ACCESS MODES
A Cisco ASA security appliance has four main administrative access modes:

• Monitor Mode: Displays the monitor> prompt. A special mode that enables you to update the image over the network or to perform password recovery. While in the monitor mode, you can enter commands to specify the location of a TFTP server and the location of the software image or password recovery binary image file to download. You access this mode by pressing the “Break” or “ESC” keys immediately after powering up the appliance.
• Unprivileged Mode: Displays the > prompt. Available when you first access the appliance. If the appliance is a Cisco PIX 500 series, the prompt for unprivileged mode is pixfirewall> and if the appliance is the new Cisco ASA 5500 Series, the prompt is ciscoasa>

This mode provides restricted view of the security appliance. You cannot configure anything from this mode. To get started with configuration, the first command you need to know is the enable command. Type enable and hit Enter. The initial password is empty, so hit Enter again to move on the next access mode (Privileged Mode).

• Configuration Mode: This mode displays the (config)# prompt. Enables you to change all system configuration settings. Use exit from each mode to return to the previous mode.

The (config)# mode is sometimes called Global Configuration Mode. Some configuration commands from this mode enter a command-specific mode and the prompt changes accordingly. For example the interface command enters interface configuration mode as shown below:

ciscoasa(config)# interface GigabitEthernet0/1
ciscoasa(config-if)# <– Configure Interface specific parameters